Field of the Invention
The invention relates to a de-glitch technology, and more particularly, relates to a de-glitch circuit, a de-glitch method and a short circuit protection device.
Description of Related Art
FIG. 1 is a schematic diagram illustrating an alternator 10 of the conventional art. The alternator 10 can be applied in cars, trains or other devices capable of providing a mechanical energy. The alternator 10 is commonly disposed with a power module 12, a rectification circuit 13 and a voltage regulator 14 inside. The power module 12 inside the alternator 10 can transform the mechanical energy into an Alternating Current (AC) power. The rectification circuit 13 is configured to convert the AC power into a Direct Current (DC) power, and the DC power can be provided to a load circuit (e.g., an indicator 20, a battery 30 and/or a load 40 as depicted in FIG. 1). The voltage regulator 14 is configured to regulate a voltage level of the DC power outputted by the rectification circuit 13. In general, alternator 10 adopts a three-phase or six-phase full wave rectification, wherein one phase AC power (also known as a phase signal) in a multi-phase AC power outputted by the power module 12 is connected to a P terminal of the voltage regulator 14. In some specific applications such as a diesel vehicle or a large-sized vehicle, the phase signal connected to the P terminal of the voltage regulator 14 is outputted to the load circuit (e.g., a load 50 depicted in FIG. 1) through a W terminal of the voltage regulator 14.
Generally, the voltage regulator 14 is also disposed with an indicator switch SW. The indicator switch SW has one terminal connected to a ground voltage and another terminal connected to one terminal of the indicator 20 through an indicator pin L of the voltage regulator 14. Another terminal of the indicator 20 can be connected to a system voltage B+. Generally, the system voltage B+ is a DC voltage. The voltage regulator 14 can control the indicator switch SW to thereby control an on/off state of indicator 20. Accordingly, the indicator 20 can present state information of the alternator 10.
In some unexpected scenarios, the indicator pin L may be short-circuited to an unexpected voltage source. When a short circuit event occurs on the indicator pin L (e.g., the indicator pin L is accidentally in direction connection with the system voltage B+) and sustains for over a confirmation time, the voltage regulator 14 of the alternator 10 can activate a protection mechanism to turn off the indicator switch SW, so as to prevent the indicator switch SW from burn-out. If the short circuit event does not sustain for the confirmation time, the voltage regulator 14 of the alternator 10 will not activate the protection mechanism. The confirmation time can prevent the protection mechanism from being mistakenly triggered by noise signals.
In an initializing period of the indicator 20 (approximately 20 milliseconds or longer), an initial resistance of the indicator 20 is very small due to low temperature. Only after the initializing period is ended, the resistance of the indicator 20 begins to rise from the initial resistance to a normal resistance due to increasing temperature. In the initializing period when the indicator 20 is activated, the protection mechanism of the indicator switch SW may be mistakenly triggered because the initial resistance of the indicator 20 is very small. Considering such characteristic of the indicator 20, the confirmation time must be greater than the initializing period during which the indicator 20 is activated, so as to prevent the protection mechanism of the indicator switch SW from being mistakenly triggered because of the small initial resistance of indicator 20. In general, the confirmation time can be set to 30 milliseconds or even longer.
Moreover, it is also possible that the indicator pin L may be unexpectedly short-circuited to an AC voltage source. For instance, the indicator pin L of the alternator 10 may be short-circuited to the W terminal. A voltage outputted by the W terminal is an AC voltage 11, and a pulse width of the AC voltage 11 may be less than the confirmation time (30 milliseconds) of the protection mechanism of the indicator switch SW. When the pulse width of the AC voltage 11 outputted by the W terminal is less than the confirmation time, the protection mechanism of the indicator switch SW will not be triggered/activated.
FIG. 2 is a schematic diagram illustrating a temperature variation of the indicator switch SW when the indicator pin L is short-circuited to the W terminal in FIG. 1. A horizontal axis depicted in FIG. 2 represents time. A vertical axis of an upper-portion curve of FIG. 2 represents a voltage of the W terminal of the alternator 10. A vertical axis of a middle-portion curve of FIG. 2 represents a voltage of the indicator pin L of the alternator 10. A vertical axis of lower-portion curve of FIG. 2 represents a temperature of the indicator switch SW of the alternator 10. As described above, the confirmation time of the protection mechanism of the indicator switch SW must be greater than the initializing period of the indicator 20, so as to prevent the protection mechanism of the indicator switch SW from being mistakenly triggered because of the small initial resistance of indicator 20. However, when the short circuit event occurs (when the indicator pin L is short-circuited to the W terminal), because a pulse width 201 of the AC voltage 11 outputted by the W terminal is less than the confirmation time of the protection mechanism of the indicator switch SW, the protection mechanism of the indicator switch SW will not be triggered/activated. In the situation where the protection mechanism of the indicator switch SW is not triggered/activated, the short circuit event can cause a large amount of current to intermittently (periodically) flow through the indicator switch SW, resulting in a continuous rising of temperature at the indicator switch SW. Eventually, the indicator switch SW may be burn-out due to overly-high temperature.